The present invention relates to a contour emphasizing circuit and a contour emphasizing method which are used in image processing.
In a conventional contour emphasizing circuit used for image processing, a differential process is applied to an inputted signal and the resultant signal is added to the original inputted signal.
However, in the conventional contour emphasizing circuit, signals before and behind the contour part of an image are also amplified and emphasized. The emphasized region becomes wider than the contour part. Consequently, the image has reduced sharpness. Hence it is difficult to obtain a clear image with the conventional contour emphasizing circuit.
Further, the differential signal including noise or ringing is added to the original inputted signal, therefore, when the degree of the contour emphasizing is increased, there is a problem in that the signal to noise ratio (SNR) of a signal outputted from the contour emphasizing circuit is deteriorated.
It is therefore an object of the present invention to provide a contour emphasizing circuit and a contour emphasizing method in which an image having sharpness and a clear image can be obtained.
According to a first aspect of the present invention, for achieving the objects mentioned above, there is provided a contour emphasizing circuit. The contour emphasizing circuit provides a contour emphasizing signal generating means which outputs a delayed video signal, a contour emphasizing signal, and a plurality of differential signals by processing an inputted video signal, a signal level difference detecting means to which the plurality of differential signals outputted from the contour emphasizing signal generating means are inputted and which outputs a signal selecting control signal, and a signal selecting means to which the delayed video signal, the contour emphasizing signal, and the signal selecting control signal are inputted and which mixes the delayed video signal with the contour emphasizing signal in an arbitrary ratio and outputs a video output signal or which selects the delayed video signal or the contour emphasizing signal and outputs the selected signal as a video output signal.
According to a second aspect of the present invention, in the first aspect, the contour emphasizing signal generating means provides a plurality of delaying means which delays the inputted video signal and generates a plurality of delayed video signals in which one of the plurality of delayed video signals is a delayed video signal that the inputted video signal is delayed and the other of the plurality of delayed video signals is a delayed video signal that the delayed video signal is further delayed, a plurality of primary differential signal outputting means in which the inputted video signal and one of the plurality of delayed video signal are inputted and outputs a differential signal, and one and the other of the plurality of delayed video signals are inputted and outputs another differential signal, a secondary differential signal outputting means to which the differential signals outputted from the plurality of primary differential signal outputting means are inputted and outputs a secondary differential signal, and an adding means to which the further delayed video signal and the secondary differential signal are inputted and outputs the contour emphasizing signal.
According to a third aspect of the present invention, a contour emphasizing method provides the steps of; delaying an inputted video signal and outputting a delayed video signal, delaying the delayed video signal and outputting a further delayed video signal, applying primary differential to the inputted video signal and the delayed video signal and outputting a primary differential signal, applying primary differential to the delayed video signal and the further delayed video signal and outputting another primary differential signal, applying secondary differential to the primary differential signals and outputting a secondary differential signal, adding the further delayed video signal and the secondary differential signal and outputting a contour emphasizing signal, comparing the primary differential signals and detecting changing range of inputted video signal level and outputting a signal selecting control signal, and outputting a video signal by mixing the further delayed video signal with the contour emphasizing signal obtained at the adding process in an arbitrary ratio or by selecting the further delayed video signal or the contour emphasizing signal based on the signal selecting control signal.